Conventional electrosurgical instruments and techniques are widely used in surgical procedures because they generally reduce patient bleeding and trauma associated with cutting operations, as compared with mechanical cutting instruments and the like. Conventional electrosurgical technologies may be classified as being monopolar or bipolar. Monopolar techniques rely on external grounding of the patient, where the surgical device defines only a single electrode pole. Thus, the electric current must pass through the patient to reach the external grounding pad. Bipolar devices have two electrodes that are located in proximity to one another for the application of current between their surfaces. By being located in proximity to one another, bipolar devices have the advantage that current need not be passed through the body, but rather only between the two electrodes.
Conventional bipolar devices are commonly used to maintain or create hemostasis. Electrosurgical energy passing between the electrode poles through tissue promotes coagulation and thereby reduces bleeding. A historic limitation of these devices has been their inability to cut tissue, which greatly limits their utility.
Recently, RF bipolar generators and tools have been developed which cut tissue through the use of plasma. These systems employ a conductive fluid supply which is converted to a plasma ‘bubble’ on a portion of the electrode tip through the application of RF electrosurgical current. Tissue that contacts the plasma bubble experiences rapid vaporization of its cellular fluid, thereby producing a cutting effect.
Creation of a plasma ‘bubble’ in the conductive fluid media at the electrode tip requires a very high current density. As such, unlike conventional bipolar instruments, the electrode poles on these devices are not of generally the same size. Rather, one of the poles (active) is significantly smaller than the other (return). This configuration allows for current density sufficient to form plasma only at the active pole. When driven at reduced voltage levels that are not sufficient to form and maintain a plasma bubble, these devices can be used as conventional bipolar devices to direct current through a defined area of tissue. Thus, a single bipolar instrument is capable of both cutting and the creation/maintenance of hemostasis.
Known bipolar cutting devices employ an active electrode(s) at the distal tip of the instrument, and a return electrode in the vicinity of the distal tip, but proximal of the active electrode, as shown in FIG. 1. The active electrode is completely exposed (uninsulated) at the distal tip, and electrical energy flows from this electrode to the return electrode as indicated generally by the arrows. As the active electrode is completely exposed and unprotected, any error while placing or manipulating the device can result in unwanted damage to surrounding tissue.
It would thus be desirable to provide an improved tip design that eliminates or minimizes the potential for collateral tissue damage, thereby improving the safety and effectiveness of the device.